Specialist article in KÄLTE KLIMA AKTUELL
Cooling of laser welding robots
In 2018, automotive supplier Läpple Automotive invested in sustainable and future-proof process technology at its headquarters in Heilbronn with the construction of a new 5,000 m² production hall. The automotive supplier attaches particular importance to maximum availability of process cooling. Two redundant propane (R290) cold brine units in conjunction with a free cooler ensure the cooling supply for the modern robot technology. In future, body parts for a Stuttgart-based sports car manufacturer will be manufactured in the new production hall at Läpple. In order to meet the high quality standards of its customers, Läpple relies on the use of fully automated laser welding robots. The welding tools must be permanently cooled to ensure precise processing of the body parts. High reliability and redundant design are essential.
PROPANE INSTEAD OF R410A
The original planning concept at the tender stage envisaged implementation with the conventional refrigerant R410A. In discussions with the customer and planner, the contractor Kratschmayer Luft-Wärme Klima GmbH from Waldenburg examined the advantages and disadvantages of the planned refrigerant compared to propane, so that the decision was ultimately made in favor of the future-proof and sustainable propane variant. The decisive criteria were market availability and expected price trends. First and foremost, a system with maximum availability requires the reliable long-term availability of the refrigerant.
WELL THOUGHT-OUT SAFETY CONCEPT
The initial skepticism as to whether Läpple wanted to place a hazardous substance with an explosion risk on the factory premises with the refrigerant propane was defused by the well thought-out safety concept from Kratschmayer and the manufacturer of the propane systems, Skadec. First of all, the cold brine sets are designed as a compact unit for outdoor installation. This means that the danger zone is outside the building. The compact design means that a small amount of refrigerant is sufficient. The Skadec propane machines are equipped with multi-stage gas warning sensors as standard, which detect even the smallest quantities of propane. When gas is detected, the inside of the machine housing is specifically ventilated to prevent explosive gas mixtures or to dissolve gas pockets. The extracted air is blown out through a duct above the machine. Compared to the tender, the EER of the cold brine sets was increased to 3.93 by using propane and optimizing the component design, which is significantly higher than the previously required efficiency.
REDUNDANT REFRIGERATION CONCEPT
The two redundant cold brine units each operate on two refrigeration circuits with one compressor each. Both refrigeration circuits are equipped with an electronic expansion valve and transfer heat to the process medium via the shared plate heat exchanger. Each circuit has its own condensing coil with individually controllable EC fan. One compressor is equipped with a frequency converter so that a capacity adjustment between 30-100 % is possible. The total installed cooling capacity is 2 x 100 kW, with a demand of 100 kW. In winter, the process cooling can also be provided by free cooling.
BAFA FUNDING (available only for projects located in Germany)
Subsidies from the Federal Office of Economics and Export Control (BAFA) and the higher efficiency of the new concept offset the higher investment costs and shorten the payback period. The BAFA subsidy program expires at the end of 2019, and Läpple had the support of the system manufacturer for the application process.
SERVICE-FRIENDLY DEVICES
The connection between Skadec and the specialist trade can be seen in the many practical and clever improvements to the cold brine sets at Läpple. Improved design elements include, for example, the control cabinet door, which also functions as a rain cover, and the service-friendly component arrangement. The user interface of the touch display is clear and intuitive and makes commissioning and servicing much easier. As the machines are developed on the basis of practical experience, Skadec benefits from the experience and suggestions for improvement of the Kratschmayer assembly team and service technicians. The knowledge gained from this flows directly into further development. This significantly increases overall efficiency.
CONTROL
In terms of control technology, the redundant design is represented by a master and slave machine. On request, the master machine determines which machine goes into operation based on the operating hours. This then regulates itself or switches on the free cooler independently. The slave machine automatically jumps into the master role if this fails. In the event of a communication failure of the hardware and TCP/IP connection, both machines switch on. If one cooling circuit fails, the active machine uses the second circuit to regulate the output. The regulation and control software monitors all relevant process values for maximum operational reliability. This allows faults caused by irregularities in operation to be detected at an early stage. The designated service partner then receives an e-mail so that short intervention times can be achieved. In the event of a fault, the emergency mode implemented keeps the cooling system running for as long as possible with the maximum available cooling capacity by analyzing various process parameters. The integrated data logger records all relevant process parameters. With the help of the remote maintenance router, the Kratschmayer technicians supported the fitters from the office during commissioning.
